1. Field of the Invention
The present invention relates to a viewing apparatus and a computer-readable medium.
2. Description of Related Art
In image viewing, an adjustment of light reaching to eyes of a user from an image (e.g., polarization) is performed. A method has been known in which a hidden image provided in an image in advance emerges by the adjustment so that the image is visible. This method may be applied so that a hidden image included in the image displayed on the image display apparatus can be viewed only when an exclusive image display apparatus is combined with a polarization lens. There is a display system to provide the viewing of a hidden image only to a user having a polarization lens (e.g., see Japanese Patent Application Laid-Open Publication No. 2009-169148).
However, the conventional display system has been insufficient to limit users who can view the hidden image. The reason is that even an unauthorized user who is not permitted to view a hidden image happens to be able to view the hidden image by obtaining a polarization lens by some ways.
Furthermore, in the case of the conventional display system, an image including a hidden image must be displayed by an exclusive image display apparatus. This has made it impossible to handle hidden images included in images on other media, such as an image printed on paper, not handled by the exclusive image display apparatus.